PAR-WebStart is a helper application associated with a browser. When a user clicks on a link that points to a PNLP [PAR Network Launch Protocol] launch file (a special XML file), it causes the browser to launch PAR-WebStart, which then automatically downloads, caches, and runs the specified PAR-based application.

PAR::WebStart::PNLP, for details of the PNLP file. Some utilities used here are described at PAR::WebStart::Util. Making a suitable par archive for use here is described in make_par. perlws describes how to associate PNLP files with the appropriate application to use.